This kind of ventilator is usually installed by calculating the ventilation rate from the specified number of times of ventilation, structure of house, and room space at the time of designing a house, and determining the model of ventilating apparatus in consideration of duct length and other conditions of installation work. In actual installation works, it is often required to adjust the air flow rate by inspecting the calculated air flow rate and actual air flow rate after installation. Accordingly, the ventilator main body is provided with an air flow rate adjusting unit capable of adjusting the air flow rate in two steps, such as flow rate 1 and flow rate 2, and the air flow rate is adjusted appropriately.
FIG. 6 is a schematic wiring diagram of a conventional ventilator. A ventilator main body 101 comprises a fan motor 102, a human sensor 103, an air flow rate adjusting unit 104 for changing over the air flow rate of the fan motor 102, for example, between 100% (flow rate 1) and 70% (flow rate 2) of the maximum air flow rate, and a control unit 105 for controlling power feed to the fan motor 102. Aside from the ventilator main body 101, a wall switch 106 is installed separately. The wall switch 106 includes a power switch 106a for turning on and off the power source, and a mode switch 106b for changing, over between automatic operation mode for controlling the fan motor 102 by the human sensor 103 and continuous operation mode for operating at specified flow rate. The builder of the installation work sets at flow rate 1 or flow rate 2 by the air flow rate adjusting unit 104 so as to adjust to specified flow rate after installation of the ventilator.
FIG. 7 is an operation flowchart of automatic operation of ventilator in FIG. 6. When the user sets the wall switch 106 in automatic operation, depending on the signal of the human sensor 103, the control unit 105 stops operation when the human sensor 103 does not detect presence of human body. Receiving a signal from the human sensor 103, human sensing operation or delay operation for specified time is conducted at flow rate 1 or flow rate 2.
The delay operation is intended to exhaust the moisture in the bathroom or odor in the toilet by force after the user leaves the room.
In another conventional ventilator, in the midst of ordinary ventilating operation, the ventilation flow rate is varied on the basis of detection by environmental detection sensor or the like, and the operation returns to ordinary ventilating operation when the environmental detection sensor no longer detects anything (see, for example, Japanese Patent Laid-Open Publication 9-79623).
In such ventilator, when adjusting the ventilator determined from the calculated flow rate and the actual flow rate after installation, the flow rate of fan motor is adjusted, for example, in two steps, and the adjusting interval is wide, and the flow rate may be set more than necessary, and excessive power may be wasted.
Meanwhile, when an alternating-current induction motor is used as fan motor, since the torque is small, it is hard to hold at low flow rate, and it is likely to have effects of static pressure by duct or the like. Or when strongly recommending ventilation all the time in order to keep ventilation passage by the ventilator, since the user can turn off the power feed by manipulating the wall switch, the ventilation passage may be easily closed. While bathing in the bathroom, if ventilated by force at large flow rate, cold draft may be felt by the fan motor for exhaust. Cold draft is feeling of uncomfortable coldness by the user in the bathroom due to invading air by ventilation or air stream caused by ventilation. If low flow rate operation during bathing in the bathroom is continued after the user leaves the bathroom, it takes a very long time in operation for exhausting moisture components absorbed in the building materials after use of bathroom.